If the Chargers’ joint practice with the Rams last weekend was a “dry run” for the StubHub Center, then Sunday’s 5 p.m. exhibition opener against the Seattle Seahawks is a dress rehearsal for the intimate soccer-stadium-turned-NFL-facility.

The first of two home exhibition games — the Chargers will host the New Orleans Saints on Aug. 20 — will give team and stadium officials a chance to monitor the flow of traffic outside the stadium and fans inside it, and to identify and address any problems involving concession stands, restrooms and crowd control.

About 8,000 fans attended last weekend’s practice, but a capacity crowd of 27,000 is expected Sunday night, putting the temporary home of the Chargers to an immediate test.

Parking lots open four hours and gates 3½ hours before the game. The team encourages fans to arrive early so they can park, pass through security and find their seats in time for kickoff.

Those arriving late could miss the Chargers’ first-team offense, led by veteran quarterback Philip Rivers, star running back Melvin Gordon and a fleet of talented receivers and tight ends, and defensive standouts such as edge rushers Joey Bosa and Melvin Ingram.

Chargers coach Anthony Lynn said most starters will play a series or two and that Rivers, who is beginning his 14th NFL season, will play only one series.

“We just want him to start the game with his teammates, then get him out,” Lynn said.

Even if the Chargers go three-and-out?

“Yeah,” Lynn said, “he’s probably one and done.”

The game doesn’t count, but the Chargers, who moved from San Diego in January and are trying to carve out a niche in the populated Southern California sports market, want to make a good first impression.

Even if he did, Mebane, a starter on dominant defenses that led the Seahawks to consecutive Super Bowls...

Nose tackle Brandon Mebane has no vendetta against the Seattle Seahawks and no desire to use Sunday’s preseason opener against them to show they made a mistake letting him go two winters ago.

Even if he did, Mebane, a starter on dominant defenses that led the Seahawks to consecutive Super Bowls...

(Mike DiGiovanna)

“It’s super important for us to go out there and look good as a group,” said Gordon, who rushed 254 times for 977 yards and 10 touchdowns and caught 41 passes for 419 yards and two scores last season. “It’s our first showing as an offense, as a defense. We’ve got to be together.”

The Seahawks have reached the playoffs six times and the Super Bowl twice in seven years under coach Pete Carroll, winning a championship in 2013, and they like to set the tone for the season beginning with the first snap of exhibition play.

“They take every down serious, even in the preseason,” Gordon said. “I had a chance to play against them in the preseason in my rookie year (2015), and they got me more ready than any team. I’m definitely expecting a good game, even if it’s a couple plays. I’m expecting them to play hard.”

With 90-man rosters and limited playing time for starters, Lynn’s emphasis will be on development, not winning.

“We’re more concerned about our team, evaluating our players,” Lynn said. “We’ll run our plays. We won’t do much scheming at all.

“We’re just looking for guys to help make our decisions [on who makes the team] easier. I want guys to go out there and make plays and stand out. You always find a couple in preseason that change your mind.”

Offensive coordinator Ken Whisenhunt said he sensed a “good vibe” in StubHub last weekend, and Chargers players expect the atmosphere to intensify with more fans.

“I imagine there will be a ton of energy,” left tackle Russell Okung said. “We had a really good crowd at the scrimmage, Chargers fans were excited to be there. They’re amped up. They’re ready to go. I’m excited to see it packed out.”

The maximum seating capacity for the team’s first of three seasons at StubHub will be 27,000, about 3,000 shy of what the Chargers thought they’d have. The decision to delay expansion was made in conjunction with StubHub officials and AEG, which owns and operates the stadium.

“We had the ability to go larger, but based on their recommendation, we decided to keep it at 27,000,” said A.G. Spanos, the Chargers’ president of business operations. “We value their input.

“They have so much more experience operating the building, and they felt pretty strongly about it. We didn’t want to do anything to jeopardize what we hope is the best fan experience in the NFL.”

StubHub general manager Katie Pandolfo said capacity can be increased by adding 1,000-2,000 more bleacher seats to the berm on the north side of the stadium. If the Chargers make the playoffs, the team could sell standing-room-only tickets.

“We originally talked about 30,000, but when we looked at the field seats, other concourse seating, I went back to the Chargers and said that at least for the first year, we should keep seating capacity consistent with what we’ve done for large Galaxy games,” Pandolfo said.

“We know football events are different than soccer games, a concert, a boxing match. We have to watch fans, see how they move around the concourse. We felt it was best to start with this number and have the option to expand next year.”